Digital Video Recorders (DVRs) that store video data in their hard disks have already replaced analog video recorders. DVRs include PC-DVRs based on PC architecture and embedded DVRs independent from PC architecture. It is a computer system that can independently store and process images with functions of long-time video recording, audio recording, and remote monitoring and controlling over images and voice. However, the deletion and overwrite of videos for various reasons may easily cause data loss.
Residual and deleted videos can not be extracted presently and the extraction of data stored in a DVR hard disk may suffer incompatibility as different vendors and various types of hard disks have different video stream headers.